1. Field of the Invention
This invention relates to an agricultural machine having a plow whose penetrating angle is changeable to reduce the area of a headland, and more particularly to an agricultural machine having an elongated body in an agricultural working direction, such as a bottom plowing machine, a sub soiler, a digging machine or the like, which carries out a plowing work in a deep portion of the soil.
2. Description of Related Art
A bottom plowing machine has been typically known as one of the agricultural machines for performing a plowing work. A square plowing or reciprocal plowing has been utilized as a plowing manner using the bottom plowing machine. The reciprocal plowing has been mainly utilized particularly for a reversible plowing machine, for example. When the plowing work is required for a field, the bottom plowing machine is installed to a tractor, and hauled by the tractor while it is contacted with the soil. At the initial stage of the plowing work, the bottom plowing machine is hauled by the tractor while a bottom of the bottom plowing machine is inclined at a predetermined penetrating angle with respect to the soil until it digs into a predetermined depth of soil. In order for the bottom of the bottom plowing machine to dig into the predetermined depth of soil using a suction angle inherent to shares of the bottom, the tractor has been conventionally required to move at a very long distance for the following reason.
The bottom plow is generally installed to the tractor through a three-point hitch mechanism comprising one top link and two lower links. The bottom is kept lifted in its non-operation state by the three-point hitch mechanism. In order to start the plowing operation of the bottom, the lifted bottom is downwardly descended by the hitch mechanism until it contacts the surface of the field and then the tractor is moved while the bottom is contacted with the soil. At the initial stage where the tractor starts its movement, the bottom is penetrated into the soil of the field at a shallow depth due to its weight, and thus the tractor is required to move at a sufficient plowing distance until the bottom is penetrated into the field due to its weight and reaches a predetermined deep depth which enables the plowing operation. This distance at which the tractor must move before starting the actual plowing operation is dependent on the suctional angle which is inherently set for the share of the bottom. In other words, a headland on which the tractor is turned at a time between the plowing operation for a one-line on the field and the plowing operation for another one-line on the field and then is straightly moved until the bottom is penetrated (digs) into the predetermined depth of soil, is superfluously required to perform the plowing operation. The area (width) of the headland is determined by the suction angle, and thus it is impossible to reduce the area of the headland because the suction angle is inherent to the share of the bottom and thus is invariable.
In an agricultural work using the agricultural machine as described above, even if the area of the headland which is required for the turning of the tractor (width of opening of the tractor) can be reduced, the tractor is still required to move at a sufficient distance (width) of the headland until the bottom penetrates into the predetermined depth of soil. Therefore, the total area of the headlands which are located at the both sides of the field in the plowing direction is necessarily large. Therefore, in a relatively-narrow field such as a field in Japan, a field to be actually plowed by an agricultural machine such as a plow machine is narrow, and more time is required for a treatment work for the headland after the plowing operation has been completed for the field to be actually plowed. This causes a problem in that a working efficiency is lowered as a whole. In addition, the lift height of the bottom (i.e., the height at which the bottom is lifted up from the surface of the field at maximum) is inherently determined in accordance with the performance of the tractor utilized, so that the bottom nearest to the tractor (if a multi-linked bottom type is used) cannot be lifted up at a sufficient lift height. Therefore, when an agricultural machine having an elongated body in the rear direction is used, a front or rear portion of the machine is liable to abut against a ridge when the tractor is transferred from a field to another field over the ridge, and this contact between the bottom and the ridge obstructs the running of the tractor. Particularly when the multi-linked bottom type comprising plural bottoms which are linked in series are used, the movement of the tractor over a ridge is impossible in a relatively-narrow field. In other words, a plowing machine having a large size cannot be used in a relatively-narrow field. If the angle of penetration of the bottom can be changed to a relatively large one only at the start time of the plowing work or at the time when the plowing machine is moved in its non-operation state, the bottom could easily penetrate into the field at a short moving distance of the tractor, and thus the area of the headland could be reduced. Accordingly, the plowing work could be carried out with a headland area required for the turning of the tractor and a slight distance required for the penetration of the bottom into the predetermined depth of soil, and the tractor could run on the field without suffering disturbance from an obstacle such as a ridge while plowing the field by the agricultural machine. However, as described above, the suction angle of the bottom is inherent to the bottom itself (i.e., it is fixed to an invariable one), and it is impossible to increase the suction angle of the bottom only during the plowing work, or at the normal running operation. Accordingly, the conventional agricultural machine having a plow has disadvantages in that the plow cannot be efficiently used in a narrow field, and trouble frequently occurs in the running operation of the tractor.